Reproduction of sound



Dec. 8, 1936. c. F. BISCHOFF ET AL REPRODUCTION OF SOUND Filed April 17, 1934 M w m -W M m 0 a x m 3 Mn 0 m O 5 V. .w B m .w) m 6%! 2 mmr F m I -m m w w r amed Dec. 8, 1-936 2,063,148

UNITED STATES PATENT OFFICE 2,063,148 REPRODUCTION OF SOUND Charles Frederick Bischoff, Caldwell, N. J., and Alfred Herckmans, New York, N. Y., assignors to American Telephone and Telegraph Company, a corporation of New York Application April 17, 1934, Serial No. 721,034

' 3,0laims. (Cl. 179-1) This invention relates to an improvement in to the receiver circuit by the transformer 2. The the reproduction of sound, and particularly to receiver circuit includes the head receivers R1 means for reproducing sound embracing a wide and R2 which, as pointed out hereinafter, are of range of frequencies. More specifically, the indissimilar types. Connected to the receivers are 5 vention pertains to the use of two telephone rethe inductance coil L and thecondenser C which, 5 ceivers of difierent design connected in a circuit serve to divide the frequency hand between the which enables each receiver to reproduce that two receivers. Receiver R1 is a magnetic type of weight diaphragm whose resonance is outside the ingly more power at these frequencies if the ear 2U region of 5,000 cycles per second. The frequency low frequency output of receiver R1 to compensate 5 3 of course, is obtained at the expense of over-all that its output is restricted to the frequencies were i possible t us th full output of this redenser c with the constants of L and C selected ceiver without equalization. to tune the circuit for approximately 75 cycles 35 This invention avoids difficult design problems per second. As shown by curve A of Fig. 2, the as w ll'as th s of h p w r amplifi rs by output of this receiver is then fairly uniform 40 frequency band and the other over the rest of the in the leakage loss with the increase in frequency. 40 frequency band. These receivers are connected As shown by curve B of that figure, the output in a selective circuit which transmits to each that of receiver R2 in the region of 100 cycles per secpart of the band for which it is the more efiicient. 0nd is reduced, due to the high impedance of the might be termed compensation as opposed to curves A and B, it will be seen that as the output 45 the usual method of equalization. of R1 falls off, that of R2 rises until at about 600 This invention will be clearly understood from cycles per second both receivers deliver equal the following description, when readin connecamounts of energy. From 600 tea-1,000 cycles retion with the attached drawing, of which Figure 1 ceiver R2 delivers an increasing proportion of the shows schematically a form of circuit embodying total energy until at 1,000 cycles and beyond, all 50 circuit of Fig. 1, serves to make clear the nature arrangement of the drawing is shown by curve of this invention. 0', which shows fairly uniform response through In Fig. 1 the speech input circuit l is connected the entire range of frequencies.

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uniform frequency response the frequency content of the received program is divided between two receivers. The listener wearing the two receivers can detect this division of sound energy, particularly with certain types of programs, but this in no way interferes with his reception or appreciation of the program. When connected to a high quality circuit such as a broadcasting network the quality of the received program compares favorably with that of the best loudspeaker or combination of loudspeakers available. An attendant monitoring on a circuit with these receivers would have no difficulty in detecting trouble due to -cycle induction or high-frequency noise.

The invention described herein is not limited to the particular circuit shown on the drawing, which is used merely for the purpose of illustrating the principles involved, but may be embodied in a large variety of circuits using head receivers designed for different frequency ranges.

What is claimed is' 1. In a sound-reproducing system the combi- I nation with a sound-reproducing device the freof substantially uniform through a portion of a given frequency range and non-uniform through the remainder of the said range, another sound-reproducing device whose frequency response is more nearly uniform than the response of the first mentioned device through the said remainder of the said range, a circuit containing an inductance coil in series with the said other sound-reproducing device, the said coiland receiver being shunted by a condenser, to form thereby an anti-resonant circuit, and the constants of the said elements of the said circuit being so chosen as to improve the frequency response of said other device in the range in which said first device is deficient, the said circuit being connected in series with the said first mentioned device so that the over-all,

response of both devices is substantially uniform. 2. In a sound-reproducing system, the combination with a pair of head-phones of an input circuit connected thereto, the first of said phones having substantially uniform frequency response throughout a portion of a given frequency range and non-uniform response through the remainder of said range, and the second of said phones having more nearly uniform response through that portion of said range in which the first phone has non-uniform response, characterized by the inclusion of an anti-resonant circuit in 1 series with the first phone, the said circuit comprising an inductance in series with the second phone, and a condenser shuntedacross said inductance and said second phone, the constantsof the inductance and condenser being so chosen as to render more uniform the response of the second phone through the said remainder of the range and to simultaneously reduce the elfectiveness of the first phone in the same portion of the range in which an improvement is effected in the and condenser being so chosen as to improve the response of said magnetic type receiver through all or a portion of its range and to simultaneously reduce the response of the receiver of the moving-coil type in the same frequency range in which the response of the magnetic receiver has been improved.

C '1. BISCHOFF.

AII'RED 

